/**
*      author: Y_Yao
*      created: 2024-11-22 20:29:41
**/

#include<bits/stdc++.h>

#define int LL
using namespace std;
using LL = long long;
const LL LLINF = 1e18;
const int INF = 0x3f3f3f3f;
const int N = 2e5 + 7;
int a[N];

void solve()
{
    int n;
    cin >> n;
    for(int i = 1;i <= n;i++)
    {
        cin >> a[i];
    }

    int ret = 0;
    for(int i = 1;i <= n - 1;i++)
    {
        if(a[i] == a[i+1])
        {
            int ans = 0;
            int left = i,right = i + 1;
            unordered_set<int> hash;
            while(left >= 1 && right <= n && a[left] == a[right] && !hash.count(a[left]))
            {
                hash.insert(a[left]);
                left += 2;
                right += 2;
                ans += 2;
            }
            i = left - 3;
            ret = max(ans,ret);
            if(left == n + 1) break;
        }
    }

    cout << ret << endl;
}

signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);

    int t = 1;
    //cin >> t;
    while(t--)
    {
        solve();
    }
    return 0;
}